bus/bbc/rom: Added support for the Gemini DataGem ROM carrier board.

scripts/src/bus.lua

@@ -543,6 +543,8 @@ if (BUSES["BBC_ROM"]~=null) then
 		MAME_DIR .. "src/devices/bus/bbc/rom/ram.h",
 		MAME_DIR .. "src/devices/bus/bbc/rom/nvram.cpp",
 		MAME_DIR .. "src/devices/bus/bbc/rom/nvram.h",
+		MAME_DIR .. "src/devices/bus/bbc/rom/datagem.cpp",
+		MAME_DIR .. "src/devices/bus/bbc/rom/datagem.h",
 		MAME_DIR .. "src/devices/bus/bbc/rom/dfs.cpp",
 		MAME_DIR .. "src/devices/bus/bbc/rom/dfs.h",
 		MAME_DIR .. "src/devices/bus/bbc/rom/genie.cpp",

src/devices/bus/bbc/rom/datagem.cpp

@@ -0,0 +1,96 @@
+// license:BSD-3-Clause
+// copyright-holders:Nigel Barnes
+/***************************************************************************
+
+    Gemini DataGem ROM Carrier
+
+***************************************************************************/
+
+#include "emu.h"
+#include "datagem.h"
+
+
+//**************************************************************************
+//  DEVICE DEFINITIONS
+//**************************************************************************
+
+DEFINE_DEVICE_TYPE(BBC_DATAGEM, bbc_datagem_device, "bbc_datagem", "Gemini DataGem ROM Carrier")
+
+
+//**************************************************************************
+//  LIVE DEVICE
+//**************************************************************************
+
+//-------------------------------------------------
+//  bbc_datagem_device - constructor
+//-------------------------------------------------
+
+bbc_datagem_device::bbc_datagem_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
+	: device_t(mconfig, BBC_DATAGEM, tag, owner, clock)
+	, device_bbc_rom_interface(mconfig, *this)
+	, m_bank(0)
+{
+}
+
+
+//-------------------------------------------------
+//  device_start - device-specific startup
+//-------------------------------------------------
+
+void bbc_datagem_device::device_start()
+{
+	/* register for save states */
+	save_item(NAME(m_bank));
+}
+
+//-------------------------------------------------
+//  decrypt_rom
+//-------------------------------------------------
+
+void bbc_datagem_device::decrypt_rom()
+{
+	uint8_t *rom = get_rom_base();
+
+	for (int i = 0x0000; i < 0x6000; i++)
+	{
+		/* decrypt 16K and 8K ROM data lines */
+		switch (rom[i] & 0x07)
+		{
+		case 0x01: case 0x06: rom[i] = bitswap<8>(rom[i], 7, 6, 5, 4, 3, 0, 1, 2); break;
+		case 0x02: case 0x05: rom[i] = bitswap<8>(rom[i], 7, 6, 5, 4, 3, 2, 0, 1); break;
+		case 0x03: case 0x04: rom[i] = bitswap<8>(rom[i], 7, 6, 5, 4, 3, 1, 2, 0); break;
+		}
+
+		/* decrypt additional 8K ROM data lines */
+		if (i & 0x4000)
+		{
+			rom[i] = bitswap<8>(rom[i], 3, 6, 5, 4, 7, 2, 1, 0);
+		}
+	}
+}
+
+//-------------------------------------------------
+//  read
+//-------------------------------------------------
+
+uint8_t bbc_datagem_device::read(offs_t offset)
+{
+	if (!machine().side_effects_disabled())
+	{
+		/* switching zones for DataGem */
+		switch (offset & 0x3fff)
+		{
+		case 0x1ffe: m_bank = 1; break;
+		case 0x1fff: m_bank = 0; break;
+		}
+	}
+
+	if (offset & 0x2000)
+	{
+		return get_rom_base()[(offset & 0x3fff) + (m_bank << 13)];
+	}
+	else
+	{
+		return get_rom_base()[offset & 0x3fff];
+	}
+}

src/devices/bus/bbc/rom/datagem.h

@@ -0,0 +1,48 @@
+// license:BSD-3-Clause
+// copyright-holders:Nigel Barnes
+/***************************************************************************
+
+    Gemini DataGem ROM Carrier
+
+***************************************************************************/
+
+#ifndef MAME_BUS_BBC_ROM_DATAGEM_H
+#define MAME_BUS_BBC_ROM_DATAGEM_H
+
+#pragma once
+
+#include "slot.h"
+
+
+//**************************************************************************
+//  TYPE DEFINITIONS
+//**************************************************************************
+
+// ======================> bbc_datagem_device
+
+class bbc_datagem_device : public device_t,
+	public device_bbc_rom_interface
+{
+public:
+	// construction/destruction
+	bbc_datagem_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock);
+
+protected:
+	// device-level overrides
+	virtual void device_start() override;
+
+	// device_bbc_rom_interface overrides
+	virtual uint32_t get_rom_size() override { return 0x4000; }
+	virtual uint8_t read(offs_t offset) override;
+	virtual void decrypt_rom() override;
+
+private:
+	uint8_t m_bank;
+};
+
+
+// device type definition
+DECLARE_DEVICE_TYPE(BBC_DATAGEM, bbc_datagem_device)
+
+
+#endif // MAME_BUS_BBC_ROM_DATAGEM_H

src/devices/bus/bbc/rom/slot.cpp

@@ -133,6 +133,8 @@ image_init_result bbc_romslot_device::call_load()
 		else
 			memcpy(m_cart->get_rom_base(), get_software_region("rom"), size);
 
+		m_cart->decrypt_rom();
+
 		if (get_software_region("ram"))
 			m_cart->ram_alloc(get_software_region_length("ram"));
 
@@ -208,6 +210,7 @@ void bbc_romslot_device::write(offs_t offset, uint8_t data)
 #include "rom.h"
 #include "ram.h"
 #include "nvram.h"
+#include "datagem.h"
 #include "dfs.h"
 #include "genie.h"
 #include "pal.h"
@@ -229,6 +232,7 @@ void bbc_rom_devices(device_slot_interface &device)
 	device.option_add_internal("palabep", BBC_PALABEP);
 	device.option_add_internal("palabe",  BBC_PALABE);
 	device.option_add_internal("palmo2", BBC_PALMO2);
+	device.option_add_internal("datagem", BBC_DATAGEM);
 	device.option_add_internal("genie", BBC_PMSGENIE);
 	device.option_add_internal("dfse00", BBC_DFSE00);
 	//device.option_add_internal("ramagic", BBC_RAMAGIC);

src/devices/bus/bbc/rom/slot.h

@@ -138,6 +138,9 @@ public:
 	uint8_t* get_nvram_base() { return &m_nvram[0]; }
 	uint32_t get_nvram_size() { return m_nvram.size(); }
 
+	// decrypt data lines
+	virtual void decrypt_rom() { };
+
 protected:
 	device_bbc_rom_interface(const machine_config &mconfig, device_t &device);